Samurai Sentai Shinkenger

There is a lot in common with the cast of both Kenshin and Shinkenger. It's a samurai season which is another way to get interested in for, and both have a dark tone with a mix of satire.

It's the 32th sequel of the series from Super Sentai right after Engine Sentai Go-Onger which is the 31th sequel. If you would like to watch the super sentai series chronologically.

It's the 33th sequel of the series from Super Sentai right after Samurai Sentai Shinkenger which is the 32th sequel. If you would like to watch the super sentai series chronologically.

Both Red in there teams are named Takeru
Both have villains that are ancient and are from another world

It's the very first Super Sentai series what made many of it's successors possible. If you want to watch the original first season of the Super Sentai series.